1. Field of the Invention
The present invention generally relates to an improved optical arrangement for performing traceable null testing of aspheric surfaces and, in particular, relates to one such arrangement using reflective/diffractive optics.
2. Description of the Prior Art
Prior art arrangements of null testing optical components have included the use of refractive null lenses. The use of such lenses in a null testing optical arrangement results in a null testing system which is difficult to qualify because accurate knowledge of all of the lens construction parameters, such as radius of curvature, thickness, centering, surface form, material refractive index and homogeneity, is needed. The use of refracting null lenses in null testing optical arrangements also requires that the refractive lens be made from a good specimen of optical glass having well known optical properties.
The use of a diamond turned (kinoform) reflective/diffractive null optical component in the arrangement of the present invention overcomes the above identified problems associated with the qualification of the refractive lens null optical component used in prior art null testing optical arrangements. Also, the improved null testing optical arrangement of the present invention avoids the use of optical materials in the transmission of light and allows the diffractive null testing technique to be immune to homogeneity variations.
Consequently, it is highly desirable to provide an improved null test optical arrangement that overcomes the above recited drawbacks of the prior art null testing optical arrangements using conventional null testing components.